3G Jailbreaking Problem Solving Needed

Ok, I need some help or advise. I had a first gen iphone I had jailbreaked to use as a pay as you go phone with ATT. I then I had gotten a 3G iphone from an ad on craigslist. The 3G was on 2.2 and was jailbreaked as well. It came with a Gevey 3G sim. The phone worked on edge but it used up my alotted time very quickly. I decided to update the iphone to 3.0 and jailbreak and unlock it for T-mobile, getting the Sidekick plan to use. I jailbreaked the iphone with redsnow and everything seemed to go smoothly. But when I put the T-Mobile simcard in the 3G, it says invalid sim. When I put the gevey in with it it says no sim installed. The ATT sim shows edge and 3G but will not get on the internet. I can't get on my wifi to run ultrasnow, but could this be the problem? I really don't want the high cost of ATT's monthly service. What do you guys think is the problem. The T-mobile sim and the ATT sim both work in the first gen iphone, and I can get the sims to work on the phones for calls but not internet. Any help would be appreciated.

Why can't you go on wifi? It says invalid sim because you don't have ultrasn0w installed (aren't unlocked). Fine a place with free wifi and get Ultrasn0w installed. The Gevey sim you have is probably not the most up to date version and therefore not compatible with OS 3.0.